DMEK plus cataract surgery
Compensating for hyperopic shift may further improve refractive outcomes
In theory, combining Descemet membrane endothelial keratoplasty (DMEK) with cataract surgery should produce similar refractive results to cataract surgery alone because the graft does not change keratometry. In practice, however, a hyperopic shift frequently accompanies combined DMEK-cataract procedures.
Compensating for this shift when calculating intraocular lens power calculations may further improve refractive precision and outcomes, which are already substantially better than with the traditional penetrating keratoplasty triple procedure, Guillaume Boutillier MD of Rouen University Hospital, France, told the 37th Congress of the ESCRS in Paris.
In a retrospective, descriptive study of 133 Fuchs’ dystrophy patients undergoing combined DMEK-cataract procedures at four French centres, Dr Boutillier found the mean difference between target and post-surgical refractions was +1.21 dioptres at two months, and +1.12 dioptres at six months. Because many procedures targeted slight myopia, this left patients with a mean uncorrected refractive outcome of +0.72±1.0D. Still, corrected outcomes improved substantially from a mean 0.49±0.3 log MAR, or about 20/63, preoperatively to 0.14±0.14, or about 20/30, at two months and 0.05±0.1, or just shy of 20/20, at six months.
These results are similar to other studies of DMEK-cataract combined procedures, which report mean refractive errors after surgery ranging from +0.43D to +0.9D, Dr Boutillier said (Laaser K et al. Am J Ophthalmol.2012;154:47-55. Schoenberg ED et al. J Refract Surg.2015;41:1182-9. Girbardt et al. Ophthalmal Z Dtsch Ophthalmol Ges. 2016;113:213-6). But he believes it is possible to do better.
“We need to use compensation means to avoid this refractive error.”
Dr Boutillier suggested several strategies to compensate for this hyperopic shift that could further improve refractive precision. The simplest may be to adjust the target refraction to the myopic side by an amount similar to the anticipated hyperopic shift.
Adjusting keratometry may be another approach. One study found that subtracting 1.19D on both axes produced an average final error of -0.23D in combined Descemet stripping automated endothelial keratoplasty (DSAEK)-cataract procedures (de Sanctis U et al. Am J Ophthalmol. 2013 Aug;156(2):254-259).
Similarly, optimising the manufacturer’s A constant for DSAEK-cataract combined procedures significantly improved IOL power predictive accuracy, from a mean absolute error of 1.09±0.63D to 0.61±0.4D (Bonfadini G et al. Ophthalmology. 2013 Feb;120(2):234-9). A similar adjustment might be made for DMEK combined procedures, Dr Boutillier said.
DMEK-cataract is a safe and effective technique for treatment of Fuchs’ dystrophy associated with cataract, Dr Boutillier concluded. But frequent hyperopic shifts occur that must be compensated for to achieve the goal of emmetropia.
This hypermetropic shift is almost constant but with variable values. It would be interesting to understand which parameters are responsible for this shift and therefore which patients are most at risk of postoperative refractive error, Dr Boutillier added.